Several patents, patent applications and publications are cited in this description in order to more fully describe the state of the art to which this invention pertains. The entire disclosure of each of these patents, patent applications and publications is incorporated by reference herein.
Glass laminated products have contributed to society for almost a century. Beyond the well known, every day automotive safety glass used in windshields, laminated glass is used as windows for trains, airplanes, ships, and nearly every other mode of transportation. Safety glass is characterized by high impact and penetration resistance and does not scatter glass shards and debris when shattered. These, together with other characteristics set forth below, are among the commonly recognized beneficial properties of safety glass.
Safety glass typically consists of a sandwich of two glass sheets or panels bonded together with an interlayer of a polymeric film or sheet, which is placed between the two glass sheets. One or both of the glass sheets may be replaced with optically clear rigid polymeric sheets, such as sheets of polycarbonate materials. Safety glass has further evolved to include multiple layers of glass and polymeric sheets bonded together with interlayers of polymeric films or sheets.
The interlayer is typically a relatively thick polymer sheet, which exhibits toughness and bonding ability to provide adhesion to the glass in the event of a crack, crash or other physical insult. In general, it is desirable that these polymeric interlayers possess a combination of characteristics including very high optical clarity, low haze, high impact resistance, high penetration resistance, excellent ultraviolet light resistance, good long term thermal stability, excellent adhesion to glass and other rigid polymeric sheets, low ultraviolet light transmittance, low moisture absorption, high moisture resistance, and excellent long term weatherability, among other requirements.
A more recent trend has been the use of glass-laminated products in the construction of homes and office structures. The use of architectural glass has expanded rapidly over the years as designers incorporate more glass surfaces into buildings. Concomitantly, threat resistance has become an ever-increasing requirement for architectural glass laminated products. Thus, some newer products are designed to resist both natural and man-made disasters. Examples of these products include the recent developments of hurricane resistant glass, now mandated in hurricane susceptible areas; theft resistant glazing; and the more recent blast resistant laminated glass products designed to protect buildings and their occupants. Some of these products have great enough strength to resist intrusion even after the glass has been broken, for example, when a glass laminate is subjected to high force winds and impacts of flying debris as occur in a hurricane or where there are repeated impacts on a window by a criminal attempting to break into a vehicle or structure.
Society continues to demand more functionality from laminated glass products beyond the safety and security characteristics described above. One area of need is the reduction of energy consumption within the structure, such as an automobile or building, to which the laminated glass is applied. One approach to energy conservation is to reduce the transmission of radiation that tends to heat the interior of the structure. For example, some of the energy otherwise needed to air-condition a building may be conserved, if the temperature of the interior remains cooler because less solar radiation reaches the interior.
The sun's energy strikes the earth over a wide spectral range from 350 nm to 2,100 nm in wavelength. Nearly half of the sun's energy is within the near infrared region of the spectrum, 780 nm to 2,100 nm. Removing the energy from the visible region (380 nm to 780 nm) would sacrifice visual transparency through windows and, therefore, detract from one of the advantages of windows. However, since the human eye does not sense the near infrared region, attempts have been made to prevent the transmission of the energy from the near infrared region through glass laminates by modifying the glass and/or the polymeric interlayer, by the addition of further layers or by combinations of these approaches.
Liquid crystals are known to appear in many different forms, including the smectic, nematic and twisted nematic (or cholesteric or chiral nematic) forms. A comprehensive description of the structure of liquid crystals in general, and twisted nematic liquid crystals in particular is given in “The Physics of Liquid Crystals,” P. G. de Gennes and J. Prost, Oxford University Press, 1995. Twisted nematic liquid crystalline materials are also disclosed in, for example; U.S. Pat. Nos. 3,679,290; 4,637,896; 6,300,454; 6,417,902; 6,486,338 and references disclosed therein. The presence of a chiral moiety within the liquid crystalline material induces the existence of twisted nematic phases. The chiral moiety can either be present in the liquid-crystalline molecule itself or can be added as a dopant to a nematic phase, thereby inducing the twisted nematic mesophase.
Liquid crystalline materials have been considered for use in glazings to control solar radiation. Devices that incorporate micellar liquid crystal materials (discrete particles of liquid crystal materials), within matrix materials generally exhibit haze at unacceptable levels for a transparent glazing. Continuous coatings and films of liquid crystalline materials (nonmicellar liquid crystalline materials), have been disclosed in U.S. Pat. Nos. 3,679,290; 5,731,886; 5,506,704; 5,793,456;; 6,831,720; 6,630,974; 6,661,486; 6,710,823; 6,656,543; and 6,800,337. Liquid crystalline materials have also been used in window glazing units, as described in U.S. Pat. Nos. 5,156,452; 5,285,299; 5,940,150; 6,072,549; 6,369,868; 6,473,143; and 6,633,354, for example.
It is desirable to have a low-haze glazing unit that is effective in reducing the transmission of light, particularly light having wavelengths longer than those in the visible region, and that is also an effective safety glass unit.